1. Field of the Invention
The present invention relates to a method for effectively preparing at low cost a nanoscale size (10−6-10−9) particle comprising a carbon nanohorn or extremely short monolayer carbon nanotube containing carbon, such as, graphite, activated carbon, amorphous carbon, resin etc., as main components and an apparatus for preparing the same. The present invention is particularly applicable to the production of a mixture for a secondary battery electrode or fuel battery electrode. The present invention also relates to a novel nanocarbon substance.
The term “carbon nanohorn” used herein is a carbon nanoparticle having a shape of a graphite sheet that is rounded conically with a closed peak (see: Unexamined Japanese Patent Publication (Kokai) No. 2001-64004).
The term “extremely short mono-layer carbon nanotube” used herein is defined as a mono(single)-layer carbon nanotube having a length several times to several tens times the diameter. Concretely, it is a nanometer size mono-layer tube having a diameter of 0.7 nm to 5 nm and length of 3 nm to 100 nm comprising a graphite sheet having a carbon six-membered ring as a main structure. By virtue of such size, the extremely short monolayer carbon nanotube is suitable for a capsule of nano-fine particle (a magnetic fine-particle encapsulated anticorrosive magnetic material, fine-particle for magnetic memory, arithmetic element by mobile of encapsulated fine particle, etc) or ion conductor, such as an electrolyte particularly for fuel battery, provided chemical modification of surface is required in case of ion conductor.
Similarly, the term “carbon nano-fine particle” used herein is defined as a fine particle comprising, as a constituting member, a carbon nanomaterial, such as a carbon nanohorn or extremely short mono-layer carbon nanotube. This is because the carbon nanohorn or extremely short mono-layer carbon nanotube do not exist independently, but they aggregate in fine particle. Further, a fullerene, nanopolyhedron, mono-layer nanocapsule, nanographite piece, foamed carbon exist as fine particles. Furthermore, there is a case where a long mono-layer carbon nanotube, multi-layer carbon nanotube exists.
The fullerene, and nanocapsule as well as extremely short carbon nanotube are considered as the same material. One difference among them is size. The size of the mono-layer nanocapsule or extremely short carbon nanotube is larger than that of the fullerene. The difference between the mono-layer nanocapsule and extremely short monolayer carbon nanotube is that the main part of the latter is a straight tube or may be continuously connected tubes having different diameters, while the former nanocapsule is not necessarily straight, but closed like a shell.
Similarly, the term “nanocarbon material” used herein is defined as a monolayer carbon nanotube, multi-layer carbon nanotube, carbon nanofiber, carbon nanohorn, fullerene, or mixture thereof.
2. Description of the Related Arts
The carbon nanohorn is a conical-shaped carbon nanomaterial (see Unexamined Japanese Patent publication No. 2001-64004.) The carbon nanohorn is produced in aggregate. The size of aggregated fine particle of the carbon nanohorn is approximately 100 nm.
The carbon nanohorn is usually produced by means of laser evaporation of solid graphite single substance (see Unexamined Japanese Patent publication No. 2001-64004). Such a process is as described below:
A solid graphite single substance is placed in a hermetically sealed container for a process. The container is evacuated to 10−2 Pa and below and is charged with an inert gas such as Ar etc. to reach an atmosphere of 103 to 104 Pa. The hermetically sealed container is provided with a glass window through which a laser passes. The solid graphite single substance is irradiated with a laser, such as carbon oxide gas (CO2) laser and the like, through the glass window. By virtue of irradiation with the CO2 laser, the surface of the solid graphite single substance is evaporated to form soot-like substance. An aggregated fine particle of carbon nanohorn exists in the soot-like substance.
2. Problems to be Solved by the Invention
The problems associated with the conventional method for preparing carbon nanohorn by laser evaporation are as describe below.
1) A vacuum container, evacuating apparatus, laser-introducing vacuum window and CO2 laser are necessary. Apparatus cost is relatively high. In particular, a CO2 laser is high expensive.
2) Since the production process is carried out in an Ar gas-charged hermetically sealed container, it is not suitable for continuous mass production.
3) Evacuation, Ar gas introduction, and opening to air must be repeated. Production process is long.
4) When the window for introducing the laser is contaminated with carbon soot, cleaning the window must be repeated frequently because graphite material is not irradiated with a laser having the desired power. Accordingly, the equation of conditions is difficult and such a conventional method is not suitable for continuous mass production.